Mill rolls are popular in the field of sheet metal fabrication, and are generally used to wipe contaminants from the surface of a metal sheet during or after manufacturing, or both. For example, the mill roll may have an outer diameter of 25.4 cm (10 in) and an inner diameter of 15.24 cm (6 in), and a width of 152 to 178 cm (60 to 70 in) to contact a sheet of the same or a lesser width. To remove contaminants from the surfaces of a sheet, the sheet is passed between two opposed mill rolls that compressively contact the surfaces of the sheet along its width. The mill rolls are typically either allowed to rotate freely at the same speed as the sheet, or driven in the opposite direction of the sheet to provide tension in the sheet. More importantly, in either application the mill rolls squeegee the surfaces of the sheet as the sheet passes between the mill rolls, to remove contaminants from the surfaces of the sheet.
The mill roll is generally tubular, and is disposed on a rigid cylindrical shaft that is rotatively supported, such as by opposed journal bearings, at each end of the shaft. Mill rolls may be made from one of several different materials. For example, rubber mill rolls generally consist of a resilient rubber tread that is carried on an elongate cylindrical shaft. When a sheet is passed between opposed rubber mill rolls, the rubber surfaces of the mill rolls squeegee the surfaces of the sheet to remove contaminants. Although rubber mill rolls may be desirable for some applications, they are easily defaced by protrusions in the metal sheets, which are common near a splice between the end of one sheet and the beginning of a second sheet. Once a rubber mill roll has been damaged, a cut, rip, or tear tends to allow contaminants to remain on the sheet, and therefore decreases the effectiveness of the rubber mill roll. If the cut, rip, or tear propagates along the surface of the rubber mill roll, the effectiveness of the mill roll may be further decreased.
Another type of mill roll is known as a fabric mill roll. An example of such a mill roll is disclosed in U.S. Pat. No. 4,669,163 (Lux et al.), the contents of which are incorporated by reference herein. Fabric mill rolls are resilient and relatively compressible compared to rubber mill rolls, and are made from an aligned plurality of discrete, circular mill roll discs. The mill roll discs are made of fabric (such as a nonwoven web of fibers), and each disc has a concentric central aperture, as shown in FIG. 1. In preparation for forming the mill roll, a plurality of mill roll discs 1 may be aligned and mounted on a shaft 2 as shown in FIG. 2. To consolidate the discrete mill roll discs 1 into a mill roll 3, the mill roll discs, which are typically saturated with a suitable bonding agent, are compressed and bonded together to form the mill roll, as shown in FIG. 2. For example, the individual mill roll discs may be saturated with a moisture activated adhesive, compressed under a force of approximately 20.times.10.sup.5 to 55.times.10.sup.5 Pa, and bonded together by the application of moisture to the mill roll. Collars 4 and 5 may also be provided to maintain a compressive force on mill roll 3, and to prevent mill roll 3 from moving along the length of shaft 2. The outer peripheral surface 6 of the mill roll, which is made up of the outer peripheral surfaces 7 of each of the individual mill roll discs, may be dressed, if necessary, to provide a smooth surface for contact with the surface of the sheet. The inner peripheral surfaces 8 of the individual mill roll discs collectively define central bore 9 of mill roll 3.
Fabric mill rolls have been found to be superior to rubber mill rolls for several reasons. Fabric mill rolls generally have an improved squeegee action, and are more resistant to damage because the surface of a fabric mill roll is self-healing. "Self-healing," as used herein, means that a cut or tear inflicted by a protrusion in the sheet generally will not result in a permanent defect in the face of the mill roll. That is, if the peripheral surface of one or more mill roll discs is damaged by a protrusion, the edges of the mill roll discs adjacent the damaged disc tend to expand into the area that was damaged, because of the pressure under which the discs are placed during formation of the mill roll, and due to the pressure applied to ends of the mill roll during operation. The expansion by the adjacent portions of the mill roll may take place over time (e.g. 1 to 3 hours), and after the expansion the mill roll will again tend to wipe the surface of the sheet effectively.
As described briefly above, fabric mill rolls are typically constructed by mounting dozens, hundreds, or even thousands of circular fabric mill roll discs on a shaft, as shown in FIG. 2. However, the frictional contact with the shaft may be insufficient to prevent rotation of the mill roll with respect to the shaft, which is undesirable because the frictional contact required to wipe a sheet adequately may not be present if the mill roll is free to rotate with respect to the shaft on which it is carried. It is therefore desirable to prevent the mill roll from rotating with respect to the shaft on which it is carried.
One solution to the foregoing problem is disclosed in the '163 patent referenced above. As shown in FIG. 3, a keyway 11 is formed along the length of shaft 2' and a key 12 is disposed within the keyway. The key projects radially from and extends longitudinally of the shaft. Each individual mill roll disc may then be provided with a keyway portion adjoining the center aperture, as shown in phantom lines 10 in FIG. 1, and the individual mill roll discs may be manually mounted on the keyed shaft by an operator. The resulting fabric mill roll is thereby prevented from rotating with respect to the shaft, which tends to improve the performance of the mill roll. Although this process of forming a mill roll is generally effective, a substantial amount of time and manual labor is required to place each fabric mill roll disc on the shaft, with the keyway and key aligned, to form the mill roll. For example, it can take between two and four hours for a worker to form a single mill roll comprising 2500 to 5000 mill roll discs, according to this method. It is therefore desirable to provide an easily manufactured mill roll that does not rotate with respect to the shaft on which it is mounted.